April 2, 2009

Forming curve in lower aft end of fwd. skin - 6.0 hrs.

Well, after all the work of putting the forward side skins on, it's time to take them off again. The lower aft end of this skin needs to have a curve bent into it that wraps around the bottom end of the fuselage. I'm not sure why the plans don't have you put this curve in first. It seems like an extra step with more work involved, to put the skin on and then take it back off to put the curve in. But I'm not going to question it. The skins are on now and have to come off for this step. We haven't even been instructed to drill the skins to the fuselage yet. I read ahead and there doesn't seem to be any mention of when to drill the skins to the fuselage. Nevertheless, I decided to wait with the drilling and put this curve into the skins first. Besides, there are some rivets I need to drill out first that are in the way, that I shouldn't have put in too soon.

This is the corner of the curvature, where the bend will be a sharp, almost 90-degree bend. Some builders have had cracking take place here. I definitely don't want that! So my thinking is, I should take steps to help minimize the chances of cracking here. How do I do that? Well, how about starting with some deburring and smoothing of the edges? Go back and read Section 5 of the manual, and it talks about why we deburr. It helps minimize stress in the aluminum and prevent cracking! Since it has to be done anyway, why not do it now? So I went ahead and spent some time carefully deburring the edges of the skin in this area, paying special time and attention to the corner notch. I didn't deburr the whole skin, just this area for now.

When the deburring is finished, you drill a scrap piece of angle to the skin to use as a lever of sorts to bend the skin. I used my crescent wrench to pull up on the angle's vertical flange and form the conical-shaped bend. Also seen here is my backriveting plate, used to define where the edge of the bend will be. It's all clamped to the table and you tighten your wrench on the angle and lift up to begin the bending. I spent quite a bit of time on this. The manual says go slow and take your time, and that's exactly what I did. When I thought it was about right and time to check it, there was no sign of cracking (whew!). Below is a closeup shot of the corner notch, all deburred and smooth just before starting the bend.

While the skin was off the fuselage, I took some time to drill out some rivets. This is the upper corner of the F-705 bulkhead (remember, the structure is upside down at this point). The 9 rivets to the left and below the red arrow needed to be drilled out. I shouldn't have squeezed them in place when I did, back when I was putting this bulkhead together on November 8, 2008. The reason is, they hold a big thick corner stiffener bracket in place that stiffens and strengthens this corner (you can't see it here; it's behind on the back side in this picture). The bracket is in the way of drilling and riveting the skins, so it needs to come out. It will be put back on later on, after the skins are riveted in place.

Here's the bracket in question, after drilling it out. As you can see, I managed to drill out 9 rivets without causing any damage to the parts. There are nine more rivets on the other side, for the bracket in that corner needs to be drilled out, too.

Here's the corner where this bracket sits on the back side of this bulkhead. As you can see, it's now open for drilling and riveting the skins and longeron.

While I'm drilling out rivets, there's one more on each side of the aft fuse that needs to come out. The one marked above had to come out because the forward side skin overlaps this far for a double row of rivets, and this hole needs to be open for that rivet. There's another one just like it on the other side, too. You can see I've marked it in the photo below with a small red arrow as well.

When I clecoed the skin back on the fuselage, wow! I was surprised at how well it fits. Not bad for the first attempt at bending the curve. The clecos went in without much of a hassle, and I think this is about as good as it's going to get.

Next, I drilled the skin to the F-623 corner rib. This pulled it all together nice and tight.

However, I'm not real happy with the gap on the right side. I'm going to have to look into this and see if I can somehow make it better.

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Contact me: swayze "at" europa.com (replace "at" with the @ sign... no spaces... you know the deal)